When I have mod points, I have started reading un-threaded at 0, with newest posts first. Reading newest first seems like the most important. I generally try to use up my points quickly but thoughtfully. If I start at the top (ie. oldest posts first), I usually see a few posts deserving some points before I even get half way through a topic that already has 100 or so posts. Starting at the other end gives you a chance to get to some of the fresh stuff that could still have an impact on the discussion if it becomes visible soon enough.